1. Field of the Invention
The present invention relates generally to a dry etching method. More specifically, the invention relates to a dry etching method applicable for semiconductor manufacture by performing anisotrophic etching.
2. Description of the Background Art
In the recent semiconductor technologies silicon trench etching techniques have become important in ultra-large LSI (ULSI) manufacture for development of applications for fabrication of high mega-bit DRAM, high speed bipolar device and so forth. For performing the etching process, various etching gasses have been developed and used. Typically, fluorine (F) type gas, chlorine (Cl ) type gas, or mixture thereof are used as the etching gas. For example, the Japanese Patent First (unexamined) Publication (Tokkai) Showa 63-73526 discloses an etching method utilizing SiCl .sub.4 /N.sub.2 type gas.
In the conventional dry etching method for monocrystalline silicon, a SiO.sub.2 mask is formed on the inner periphery perpendicular to the plane of a monocrystal substrate and, then, etching is performed with SiCl .sub.4 /N.sub.2 type etching gas. In this process, Si.sub.x N.sub.y which is a reaction product generated during the etching process is used as a protective layer for forming a trench.
However, this prior proposed dry etching process is still incomplete and defective in the following points.
At first, in the prior proposed process, the reaction product forming the protecting layer, can serve for obstructing etching and thus can lower the etching speed or efficiency. Furthermore, in case of a batch type etcher or in case of the making a relatively wide trench, the etching rate or efficiency can be lowered due to a loading effect. In order to solve such a problem of low efficiency, there has been proposed to use SF.sub.6 /SiCl .sub.4 /N.sub.2 type etching gas in "1988 Shuuki Obutsu" 7a-K-7. In this prior proposal, the contamination can be caused.
On the other hand, when the pattern is not possible to be formed by lithographic process and has to be patterned by a self-alignment process, the self-alignment process is performed by forming side wall by SiO.sub.2 with utilizing tetraethoxysilane and performing the etching while utilizing the thus formed side wall as a mask. In such case, the taper on the side wall may influence or cause scattering of the injected ion beam to cause a scoop or under-cut at the location immediately beneath the mask. This makes it difficult to form the desired configuration of the trench.